Von-Neumann and Harvard computer model

Von Neumann computer model

It contains three main building blocks.

1) Central Processing Unit (CPU)
     It is responsible for processing of data and ensures that programs are executed in correct order

2) Memory
   There is single memory that stores both data and instructions

3) Input-Output devices
   Input devices are used to give input to the computer. Some of the common examples are keyboard      and mouse.

These three components are connected using system bus.

Harvard computer model

Harvard computer model contains same building blocks as Von Neumann model. But there is one important difference. 
There is a separate memory for data and instruction namely- data memory and instruction memory.
Because of this, data and instructions can be fetched from memory simultaneously. This luxury is not available in Von Neumann model.

Von Neumann and Harvard computer model.

Note that input and output devices are not shown, but they are present in both the computer models.